Observed (black) and modelled (red and blue) Stokes V signatures (left) and null N profiles (right) of ζ Ori A. The blue line corresponds to a simple dipole, while the red one corresponds to a more complex field having ℓ= 3. A clear Zeeman signal is detected and consistently modelled in the Stokes V profiles. The rotational cycle of each observation (assuming a rotation period of 7 d) is written next to each profile. A 1σ error bar is also plotted left to each profile.